1. Field of the Invention
The invention relates to a weighing cell with a force introduction element and a force absorption element which are connected by means of force transmission members to an annular deformation body arranged between them. On both sides of its mid-plane, the deformation body has mechanical/electrical transducer elements arranged at an axial distance from one another and converting mechanical deformations of the body into electrical quantities.
2. Description of the Prior Art
In weighing cells of this type, the amount of force introduced is measured by means of the tangential deformations experienced by a bending ring, at the inner edge of which the load is introduced and which is supported at its outer edge on a force absorption element. The compression or expansion of surfaces of the ring which are arranged at an axial distance from one another on opposite sides of a mid-plane, when the ring bends, are absorbed by the transducer elements and converted by these into electrical measuring signals which can be amplified and displayed in a suitable way.
In one such known weighing cell (German Patent Specification No. 1,268,878), the force transmission members are thin-walled cylindrical tubular pieces which are connected at one edge to the deformation body and at the other edge to the force introduction element or the force absorption element and which transmit the force from the former to the latter tangentially in the direction of the generatrices of the cylindrical tubular pieces. Because of the high rigidity of the tubular force transmission members and as a result of the complicated deformations which these tubular pieces experience during force transmission, high restraining moments are generated. Furthermore, high stress peaks occur at the points where the tubular force transmission members merge into the deformation body. These high stresses lead, in turn, to inelastic deformations and to hysterisis phenomena and have the effect of impairing the measuring accuracy.
There is also a known weighing cell (U.S. Periodical W & M, 1987, pages 19-22), in which the force introduction element and the force absorption element are connected to one another by means of an annular disk, from which is fashioned, by means of lathe-turned recesses on the top side and on the underside, a deformation body of approximately rectangular cross-section, the height of which corresponds to the thickness of the annular disk at its inner and outer edges where the latter merges into the force introduction element and the annular force absorption element respectively. Since the annular disk is connected rigidly in terms of bending to the force introduction element on the one hand and to the force absorption element on the other hand and angular twists are possible only in the region of the lathe-turned recesses next to the deformation body, disturbing moments are transmitted to the deformation body and to the transducer elements fastened to it which are caused, for example, by an eccentric introduction of the load into the force introduction element or an eccentric mounting of the force absorption element. These disturbing forces vary, in places, the bending moment exerted on the deformation body and thus influence the tangential stresses taking effect there and originating from the load, thus leading to a falsification of the measurement result.